Carbon fibre tow

ABSTRACT

The degree of alignment of carbon fibres in a continuous carbon fibre tow is improved by applying a resin solution to the tow at a point where the tow is still travelling under the same tension and in the same direction as that in which it travelled through the furnace. Application of the resin, e.g., polyvinyl alcohol in a volatile organic solvent, may be effected by means of a porous, e.g., felt, spreader without substantially altering the direction of travel of the tow.

United States Patent n91 Kearsey 1 Get. 1, 1974 CARBON FIBRE TOW [75]Inventor: Hugh Arthur Kearsey, London,

England [73] Assignee: National Research Development Corporation,London, England [22] Filed: July 26, 1971 [21] Appl. No.: 166,233

[30] Foreign Application Priority Data July 27, 1970 Great Britain36360/70 [52] U.S. Cl. 117/46 CC, 8/1 15.6, 117/7, 117/111 D, 423/447,423/448 [51] Int. Cl B44d 3/12 [58] Field of Search 117/46 CB, 46 CC, 7;8/1 15.6; 118/47; 423/447, 448

[56] References Cited UNITED STATES PATENTS 3,273,987 9/1966 Marzocchiet al. 1 17/7 3,720,536 3/1973 Scola 423/447 Primary ExaminerWilliam D.Martin Assistant Examiner-Janyce A. Bell Attorney, Agent, orFirm-Wenderoth, Lind & Donack [57] ABSTRACT 12 Claims, 1 Drawing Figurelit FEED

CARBON FIBRE TOW This invention relates to the production of carbonfibre tows. As is well known, the standard procedure starts with apolyacrylonitrile fibre tow, and comprises the following steps:

1. An optional oxidation at a temperature in the range 200C to 275C.

2. Carbonisation at a temperature of the order of l,OC to 1,500C.

3. An optional graphitisation at a temperature in the range 2,250C to275C. I

4. An optional surface oxidation treatment. The present inventionrelates to a continuous process for the production of carbon fibres on arelatively large scale. It will be apparent that it is desirable toproduce the carbon fibres in long lengths, and indeed, for themanufacture of artefacts from the carbon fibres, the longer the lengththe better. It is therefore desirable to use as a starting material longlengths of PAN fibre. Similarly, for the sake of cheapness, it isdesirable to use a commercially available form of PAN fibre rather thanto use a special fibre .which, it will be understood, would inevitablybe more expensive. Finally, our tests have shown that taking intoaccount the inevitable shrinkage in diameter of the carbon fibres ascompared with the precursor material, it is desirable to make use of aprecursor material of about l.5-denier.

In order to use carbon fibres, the present practice is normally to usethem as a reinforcement in a matrix, and for many purposes it isextremely desirable that the carbon fibres should be available in theform of a tape or hand some 4 in. wide, since this form enables thecarbon fibres to be surface-treated if necessary and then to bepreimpregnated with the matrix material. It is relatively simplethereafter to split the wide tape up into narrower tapes should this bedesirable.

The normal manufacture of PAN fibres for conventional textile purposesresults in two possible forms of fibre, namely straight fibre andcrimped fibre which is produced by forcing the tow through a heatedstuffing box. In practice we have found that straight filament fibre hasa false twist which encourages fibre entanglement so that it isextremely difficult to spread the initially circular tow into an eventape of fibres. On the other hand, with crimped fibre, due to the finalcrimping stage which is carried out in the form of a wide band, thefibres naturally fall into the necessary tape form and therefore weprefer to use crimped fibres in the process of forming carbon fibres.However, it is necessary to remove the crimp before the fibres areoxidised, and also in practice we find that the crimped fibres arenormally provided as 3-denier or thicker fibres and so must be reducedin thickness before they form the most desirable carbon fibres.

In the process described in British Pat. Specification No. l I 10791, itis taught that at least a part of the operation is performed with thetow under tension in order to increase the ultimate tensile strength andYoungs modulus of the product. Tension is generally applied by means ofa roller assembly.

When the emerging carbon fibres reach the outlet rollers, two factorsoperate to spoil the alignment of individual fibres within the tow.Firstly, in those cases where the tow is wrapped around part of theperiphery of a roller, the tow has thickness so that some fibres passaround the roller at a greater radius than others.

Secondly, it is not practicable to apply much tension to the fibres forwinding up for storage, so that on the outlet side of the tensioningrollers, tension in the tow is relaxed.

It is an object of the present invention to improve the degree ofalignment of the carbon fibres in the tow as stored.

The present invention provides a method of producing a carbon fibre towwhich method comprises continuously drawing a'carbonisable fibre towlinearly under tension through a carbonising furnace and applying aresin solution to the carbon fibre tow, at a point where the tow isstill under tension and is still travelling in the direction in which ittravelled through the furnace, so as to retain the alignment of thecarbon fibres in the tow substantially as it emerged from the furnace.

The carbonisable fibre tow may be a polyacrylonitrile fibre tow eitherbefore or after the optional preliminary oxidation treatment. As theoxidation treatment is rather slow, it may be easier to wind up theoxidised tow, rather than to transfer it direct to the carbonisingfurnace. The oxidised fibres retain some elasticity, and the oxidisedtow can be wound up without excessive loss of alignment of theindividual fibres.

When a graphitisation and/0r surface oxidation treatment is carried outafter carbonisation, the tow is drawn successively without anyalteration in direction through the various treatment zones prior to theresin application.

The resin solution may be applied to the carbon fibre tow by anyconvenient method which does not involve loss of alignment of theindividual fibres. Spraying of the resin solution and application bymeans of a porous, e.g., felt, spreader are suitable methods, the latterbeing preferred. Passage of the tow through a trough of the resinsolution is not a suitable method if it involves loss of alignment ofthe individual fibres on passage round a roller.

The solvent of the resin solution is preferably rapidly volatile.Conventional organic solvents appropriate to the resin chosen, e.g.,acetone or ether, are generally suitable.

The nature of the resin is not critical to this invention. In general,the resin will be chosen with regard for the matrix which the carbonfibre tow is to reinforce. Polyvinyl alcohol, being water-soluble, issuitable for fibre intended for a further stage of wet surface treatmentor for metal composites. Epoxy resins, polyvinyl acetate systems,polyester and polyamide resins are suitable for other applications ofthe fibres. Further possible resins will be readily apparent to thereader.

The purpose of the resin application is to prevent or reduce accidentalbreakage and loss of the fibres, which are delicate and slippery, duringnormal handling. A relatively small amount of resin, e.g. from 1 to 5percent, preferably about 2.5 percent by weight on the weight of thecarbon fibre, is sufficient for this purpose. The resin coating alsogreatly improves the grip between the fibres and the rollers.

The concentration of the resin solution is not critical. As the amountof resin used is small, it may be convenient to use a rather dilutesolution, e.g. from 0.1 percent to 5 percent by weight, of the resin.

The present invention also provides apparatus for producing a carbonfibre tow, which apparatus comprises a carbonising furnace, means forcontinuously drawing a carbonisable fibre tow linearly therethroughunder tension, and means for applying a liquid to the tow, withoutsubstantially altering its direction of travel. at a point between thecarbonising furnace and the drawing means. The tension is not critical;we find it convenient to use a tension of from 2 to 16 Kg, e.g., 8 Kg,for a 160,000 3-denier filament tow.

A specific embodiment of the invention will now be described withreference to the accompanying drawing, which is a diagrammaticrepresentation of apparatus according to the invention.

The apparatus comprises a carbonisation furnace 10, a graphitisationfurnace 11, and a gaseous surface treatment zone 12 in succession,separated from each other and from the atmosphere by gas locks 13.Adjacent the final gas lock is a felt spreader l4, supplied with a 2percent solution of polyvinyl alcohol in acetone from a reservoir 15. Anextraction hood 17 is positioned next to the felt spreader 14.

In operation a tow of previously oxidised polyacrylonitrile fibres 18 isdrawn by means of a pair of driven rollers 22 and 23 from a supply (notshown) through the nip between rollers 19 and 20, which are braked toprovide the desired degree of tension in the tow between rollers 19, 20and rollers 22, 23. The tow passes successively through furnaces l and11 and treatment zone 12; past the felt spreader 14 where it picks upapproximately its own weight of the resin solution; past the extractionhood 17, where the acetone is evaporated off and the polyvinyl alcoholsets and causes the individual carbon fibres in the tow to adherelightly together; around the freely rotating roller 21 which is fittedwith a revolution counter (not shown) to measure the quantity of fibrepassing; through the nip between driven rollers 22 and 23, where thetension on the tow is relaxed; and finally on to a drum 25, where it isrolled up interleaved with paper from a supply 26.

Although the felt spreader 14 is illustrated as being above the tow 18,and the extraction hood 17 below it, it may be found more convenient toapply the resin solution to the tow 18 from below and to extractvolatile solvent from above.

The carbon fibres are slippery and difficult to handle, and it is noteasy to impart a controlled tension to the tow by means of a pair ofconventional driven pinch rollers, even when they are surfaced with anon-slip material. In the roller combination, 22, 23, which is used inthe embodiment of this invention, the roller 22 swings on a pivot 24.Also the tow, in addition to passing through the nip between the tworollers 22 and 23, passes round a substantial portion of thecircumference of each. Thus the tension in the tow increases thepressure (and hence grip) between the rollers.

I claim:

l. A method of producing a carbon fiber tow which comprises continuouslydrawing a carbonizable fiber tow unidirectionally and substantiallylinearly under tension through a carbonizing furnace to carbonize saidfiber, drawing the carbon fiber tow from said furnace so that the fibertravels in substantially the same linear direction in which it travelledthrough the furnace, applying a resin solution to the tow and allowingsaid resin to substantially set while the tow is still under tension andtravelling in substantially the said linear direction so as to preservethe alignment of the carbon fibers in the tow substantially as itemerges from the said furnace.

2. A method as claimed in claim 1, wherein the carbonizable fiber tow isa polyacrylonitrile fiber tow.

3. A method according to claim 2, wherein the carbonizablepolycrylonitrile fiber tow is subjected to a preliminary oxidationtreatment before carbonization.

4. A method according to claim 2, wherein the carbonizablepolyacrylonitrile tow is subjected to an oxidation treatment aftercarbonization.

5. A method as claimed in claim 1, wherein the carbon fiber tow issubjected to a graphitization treatment by being drawn without anyalteration in direction through the treatment zone or zones prior to theresin application.

6. A method according to claim 5, wherein the carbon fiber tow is alsosubjected to a surface oxidation treatment by being drawn without anyalteration in direction through the treatment zones prior to the resinapplication.

7. A method as claimed in claim 1, wherein the resin solution is appliedto the carbon fibre tow by means of a porous spreader.

8. A method as claimed in claim 1, wherein the resin is applied insolution in a volatile organic solvent.

9. A method as claimed in claim 11, wherein the resin is polyvinylalcohol, polyvinyl acetate, an epoxy, polyester or polyamide resin.

10. A method as claimed in claim 11, wherein the amount of resin appliedis from 1 to 5 percent by weight of the weight of the tow.

11. A method as claimed in claim 11, wherein the resin is applied in thefonn of a solution containing from 0.1 to 5 percent by weight of theresin.

12. A method according to claim 1 wherein the carbon fiber tow issubjected to a surface oxidation treatment by being drawn without anyalteration in direction through the treatment zone or zones prior to theresin application.

1. A METHOD OF PRODUCING A CARBON FIBER TWO WHICH COMPRISES CONTINOUSLYDRAWING A CARBONIZABLE FIBER TOW UNIDIRECTIONALLY AND SUBSTANTIALLYLINEARLY UNDER TENSION THROUGH A CARBONIZING FURNACE TO CARBONIZE SAIDFIBER, DRAWUNG THE ARBON FIBER TOW FROM SAID FURNACE SO THAT THE FIBERTRAVELS IN SUBSTANTIALLY THE SAME LINEAR DIRECTION IN WHICH IT TRAVELLEDTHROUGH THE FURNACE, APPLYING A RESIN SOLUTION TO THE TOW AND ALLOWINGSAID RESIN TO SUBSTANTIALLY SET WHILE THE TWO IS STILL UNDER TENSION ANDTRAVELLING IN SUBSTANTIALLY THE SAID LINEAR DIRECTION SO AS TO PRESERVETHE ALIGNMENT OF THE CARBON FIBERS IN THE TOW SUBSTANTIALLY AS ITEMERGES FROM THE SAID FURNACE.
 2. A method as claimed in claim 1,wherein the carbonizable fiber tow is a polyacrylonitrile fiber tow. 3.A method according to claim 2, wherein the carbonizable polycrylonitrilefiber tow is subjected to a preliminary oxidation treatment beforecarbonization.
 4. A method according to claim 2, wherein thecarbonizable polyacrylonitrile tow is subjected to an oxidationtreatment after carbonization.
 5. A method as claimed in claim 1,wherein the carbon fiber tow is subjected to a graphitization treatmentby being drawn without any alteration in direction through the treatmentzone or zones prior to the resin application.
 6. A method according toclaim 5, wherein the carbon fiber tow is also subjected to a surfaceoxidation treatment by being drawn without any alteration in directionthrough the treatment zones prior to the resin application.
 7. A methodas claimed in claim 1, wherein the resin solution is applied to thecarbon fibre tow by means of a porous spreader.
 8. A method as claimedin claim 1, wherein the resin is applied in solution in a volatileorganic solvent.
 9. A method as claimed in claim 11, wherein the resinis polyvinyl alcohol, polyvinyl acetate, an epoxy, polyester orpolyamide resin.
 10. A method as claimed in claim 11, wherein the amountof resin applied is from 1 to 5 percent by weight of the weight of thetow.
 11. A method as claimed in claim 11, wherein the resin is appliedin the form of a solution containing from 0.1 to 5 percent by weight ofthe resin.
 12. A method according to claim 1 wherein the carbon fibertow is subjected to a surface oxidation treatment by being drawn withoutany alteration in direction through the treatment zone or zones prior tothe resin application.